1. Field of the Invention
The present invention relates to an A/D conversion device, a D/A conversion device, and an adjusting method. More particularly, the present invention relates to an A/D conversion device and a D/A conversion device each having a plurality of D/A converters, and an adjusting method.
2. Related Art
Charge-redistribution type A/D conversion devices have been known as disclosed, for example, in US Patent Application Publication No. 2007-132626. The A/D conversion device described in US Patent Application Publication No. 2007-132626 includes a capacity-array type main D/A converter, a capacity-array type correction D/A converter, a comparator, and a control logic.
The main D/A converter outputs an analog voltage according to data given from the control logic. The correction D/A converter is supplied with data having a resolution less than 1 LSB (least significant bit) of the main D/A converter from the control logic, and outputs an analog voltage according to the supplied data. The comparator compares an input voltage with a total voltage obtained by adding the voltage outputted from the main D/A converter to the voltage outputted from the correction D/A converter.
The control logic changes the data supplied to the main D/A converter and the correction D/A converter, and searches for data at which the input voltage is identical to the total voltage. Then, the control logic outputs to the outside the data at which the input voltage is identical to the total voltage.
In this case, the control logic provides data corrected in accordance with DNL (Differential Non-Linearity) of the main D/A converter to the main D/A converter and the correction D/A converter. More specifically, the control logic provides an integer part of data corrected in accordance with DNL to the main D/A converter. The control logic also provides a fractional part of the data corrected in accordance with DNL to the correction D/A converter. In this way, the A/D conversion device described in US Patent Application Publication No. 2007-132626 can output a voltage whose DNL is corrected with accuracy less than 1 LSB.
Moreover, there has been known an interleave type A/D conversion device including a plurality of A/D converters. There has also been known a differential type A/D conversion device that includes a positive A/D converter and a negative A/D converter and converts a differential signal from analog to digital.
An A/D conversion device including a plurality of A/D converters, such as an interleave type or differential type conversion device generates a large linearity error as a whole when gains of the plurality of A/D converters are different from one another, even if the linearity error of each A/D converter is small. Therefore, an A/D conversion device reduces a total linearity error thereof by measuring input-output characteristics of the A/D converters with high precision using a DA converter for calibration and correcting the input-output characteristics of the A/D converters on the basis of the measurement results.
However, when correcting a linearity error in this manner, it is necessary to use a D/A converter for calibration with high precision. Therefore, the A/D conversion device requires a high cost.